30 Jan 2023
 | 30 Jan 2023
Status: this preprint is currently under review for the journal ACP.

Evolution of Organic Carbon in the Laboratory Oxidation of Biomass Burning Emissions

Kevin John Nihill, Matthew M. Coggon, Christopher Y. Lim, Abigail R. Koss, Bin Yuan, Jordan E. Krechmer, Kanako Sekimoto, Jose-Luis Jimenez, Joost de Gouw, Christopher D. Cappa, Colette L. Heald, Carsten Warneke, and Jesse H. Kroll

Abstract. Biomass burning (BB) is a major source of reactive organic carbon into the atmosphere. Once in the atmosphere, these organic BB emissions, in both the gas and particle phases, are subject to atmospheric oxidation, though the nature and impact of the chemical transformations are not currently well constrained. Here we describe experiments carried out as part of the FIREX FireLab campaign, in which smoke from the combustion of fuels typical of the Western US was sampled into an environmental chamber and exposed to high concentrations of OH, to simulate the equivalent of up to two days of atmospheric oxidation. The evolution of the organic mixture was monitored using three real-time time-of-flight mass spectrometric instruments (a proton transfer reaction mass spectrometer, an iodide chemical ionization mass spectrometer, and an aerosol mass spectrometer), providing measurements of both individual species and ensemble properties of the mixture. The combined measurements from these instruments achieve a reasonable degree of carbon closure (within 15–35 %), indicating that most of the reactive organic carbon is measured by these instruments. Consistent with our previous studies of the oxidation of individual organic species, atmospheric oxidation of the complex organic mixture leads to the formation of species that on average are smaller and more oxidized than those in the unoxidized emissions. In addition, comparison of mass spectra from the different fuels indicates that the oxidative evolution of BB emissions proceeds largely independent of fuel type, with different fresh smoke mixtures ultimately converging into a common, aged distribution of gas-phase compounds. This distribution is characterized by high concentrations of several small, volatile oxygenates, formed from fragmentation reactions, as well as a complex pool of many minor oxidized species and secondary organic aerosol, likely formed via functionalization processes.

Kevin John Nihill et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-857', Anonymous Referee #1, 23 Feb 2023
  • RC2: 'Comment on acp-2022-857', Anonymous Referee #2, 11 Mar 2023

Kevin John Nihill et al.

Kevin John Nihill et al.


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Short summary
In this work, we collect emissions from controlled burns of biomass fuels that can be found in the Western US into an environmental chamber in order to simulate their oxidation as they pass through the atmosphere. These findings provide a detailed characterization of the composition of the atmosphere downwind of wildfires. In turn, this will help to explore the effects of these changing emissions on downwind populations, and will also directly inform atmospheric and climate models.